As pointed out by C. J. Date, "A Guide to DB2", Addison-Wesley Publishing Co., 1984, at page 7 thereof, "A relational data base is a data base that is perceived by its users as a collection of tables and nothing but tables". In this regard, Adiba and Lindsay, "Data Base Snapshots", IBM Research Report RJ 2772, Mar. 7, 1980, noted that relational data base management systems provide an interface permitting users and application software to access the contents of a time-varying set of relations or tables. Such a management system returns or updates the current value of records selected by query language statements. These statements are either embedded in application software or are supplied by a user directly. Adiba points out that not only can users interrogate and modify records in the current data base state, but they can also insert new records and remove existing ones. Such systems also permit users to create new relations, extend the attribute set of existing relations, and destroy relations no longer needed.
One drawback of contemporary systems is that users can only operate upon the latest data base state even though applications may require or tolerate access to earlier versions of the data base. Read-only access to earlier "snapshots" of selected portions of a data base would permit such applications to view the data base "as of" a specific time without having to execute at that specific time. Also, if snapshots are not affected by updates to the "current" data base, they can be used to make selected portions of the data base "stand still" for complex applications processing without delaying update processing on a current data base state.
Adiba et al, in the remainder of their document, described the creation of a logically independent multicolumn table derived from a larger table and representing an information state frozen in time. This is the "snapshot".
For purposes of completeness, reference should be made to Daniell et al, U.S. Pat. No. 4,432,057, "Method for the Dynamic Replication of Data Under Distributed System Control to Control Utilization of Resources in a Multiprocessing Distributed Data Base System", issued Feb. 14, 1984. This reference relates to accessing copies of a table distributed among networked nodes without requiring concurrent (synchronized) updating by revising any local table with remote versions of the table as a function of node identity and time stamp ordering.